An Institute of Electrical and Electronics Engineers (IEEE) 802.16e communication system performs communication through ranging between a terminal and a base station, considering mobility of the terminal, whereas an IEEE 802.16a communication system does not consider mobility of a subscriber.
The ranging can be classified into an initial ranging, a bandwidth request ranging, and a periodic ranging according to the purpose. The initial ranging is performed to obtain synchronization between the base station and the terminal. More specifically, the initial ranging sets correct time and frequency offset between the base station and the terminal, and adjusts transmission power. The periodic ranging is periodically performed by the terminal in which the time offset and the transmission power is set through the initial ranging with respect to the base station, in order to readjust the time offset and the transmission power according to the channel state. The bandwidth request ranging is performed to request allocation of the bandwidth so that the terminal set in the time offset and the transmission power can perform actual communication with the base station.
When the terminal has no data to be transmitted on the uplink channel for a while, the periodic ranging is determined and performed.
However, when data is being continuously transmitted on the uplink channel, the terminal does not perform the periodic ranging. When such a state is continued and furthermore the terminal approaches the base station from a distance, transmission delay is reduced and the data is received to the base station faster than expected. In this case, a signal distortion may be incurred.